This invention relates to the subject of shunts for indirectly heated bimetallic strips. While especially suitable for use in circuit breakers, the shunt of this invention is useful for heating any bimetallic strip.
Circuit breakers employing indirectly heated bimetallic strips are well known. A shunt, or heater strap, is attached to one end of a bimetallic strip via brazing, rivets, or screws. Electrical current from a distribution circuit passes through the shunt. When an overcurrent condition occurs, the shunt generates heat, which is transferred to the bimetallic strip across the junction of the shunt and the bimetallic strip. The bimetallic strip is formed of two metals having different coefficients of expansion such that a free end of the bimetallic strip bends or deflects when the temperature of the bimetallic strip exceeds a predetermined temperature. If the temperature of the bimetallic strip exceeds the predetermined value, the free end of the bimetallic strip deflects to actuate a linkage interconnected to a pair of separable contacts within the circuit breaker. The linkage then opens the pair of contacts to interrupt the current and, thereby, protect a load from the overcurrent condition.
Circuit breakers employing such indirectly heated bimetallic strips are well known. However, it is desirable to reduce the response time in obtaining the desired temperature distribution through the shunt and bimetallic strip and, thereby, reduce the amount of time to trip the breaker on an overcurrent condition. It is also desirable to reduce or eliminate the temperature hot spots at the extreme ends of the shunt. Attempts have been made in the prior art to address these deficiencies, such as by creating circular, rectangular or slotted openings in the shunt. While effective to some degree, these prior art approaches still leave room for improvement.